The present disclosure relates to energetic compositions, more specifically to bonding agents in perchlorate compositions.
Energetic compositions, for example composite solid rocket propellants and other composite propellants, include solid particles dispersed in a rubbery matrix, called a binder. Solid particles that provide oxidizing chemical species to the combustion process and/or liberate energy upon decomposition are called “oxidizers.” Perchlorate containing oxidizers, such as ammonium perchlorate (AP), and nitrate containing oxidizers are used in energetic compositions. The structural properties of the energetic compositions are influenced by the bond strength between the binder and the surfaces of the solid oxidizer particles. Since the solid particles can make up a majority of the particulate matter in the composition, the bond between the binder and the oxidizer particle surfaces has a significant effect on composition's structural properties.
In addition to oxidizer particles and binders, energetic compositions can include bonding agents. Generally, a bonding agent can coat the oxidizer surface, chemically react to form an encapsulating film around the particles, and bond to the binder either chemically or adhesively, for example forming a film. If the bonding agent then has sufficient affinity for the oxidizer surface it can prevent binder-oxidizer particle separation under stress.
The structural properties of energetic compositions derive from a complex interaction of binder properties with the solid oxidizer particles. The composition properties are strongly influenced by the particle size and volumetric loading, as well as by the binder-solids bond strength. When the binder is strong relative to the binder-solids bond strength, a composition under sufficient tension can undergo separation of the binder from the oxidizer particles. The separation is sometimes referred to as de-wetting or blanching and can be followed by large extensions of the binder prior to rupture. Structurally, such a composition can be characterized by high extensibility and low tensile strength. However, when the binder-oxidizer particle bond strength is increased, as by a bonding agent, de-wetting can be prevented or forestalled, resulting in less extensibility and higher tensile strength.
In addition to binders and bonding agents, perchlorate and nitrate containing oxidizer compositions can also include burning rate catalysts, for example iron oxide (Fe2O3) or copper chromite (CuCr2O4). Although ferrocene and ferrocene derivatives can dramatically increase the burning rates of AP compositions including such burning rate catalysts, ferrocene and ferrocene derivatives can be problematic because they change concentration over time due to volatility, oxidize during storage, and severely increase friction and impact sensitivity.